For several years, I only kept around 2 cows and just recently (within the last year/year and a half) I have gotten more cattle, so I could not honestly give you a definite answer as to the most profitable setup.
There are several things to consider though. One thing is are you selling them as a breed or for meat? If as a breed, is there a demand for them in your area? I can say that I have had a 2 beef cows and would try to sell weaned calves and this did not work. Other than get experience, I lost money selling weaned calves. If you are finishing them out and selling them as a butchered product you may have better luck. This is what I am trying now with my Dexters.
One issue you may face is room and amount of grass they have assess to. I believe the Highlands are a bigger breed and will need more food than some smaller cattle. So if you have lots of room with lots of pasture, then you should not have an issue. Our grass grows really well where we live, so for larger cattle we budget one acre/cow/year.
As for the size of your herd, there are a couple of things to consider. If you want to start small with just maybe 1-5 heifers/cows, then you could think about artificial insemination. There is usually a vet that can do this and eliminates the need for a bull, but the downfalls are that you have to watch for heats and inseminations may not take each time. In our mind, with the space we had and from talking to other farmers in the area, we came to the conclusion that having around a minimum of 5 cows/heifers would be more beneficial for us to keep a bull around. So one bull to service our 9 cows/heifers works out fine. Everyone will tell you something different about when to trade out your bulls. We had it in our minds that if we were keeping all our heifers, then we would switch them out every 2-3 years to ensure that there is no inbreeding going on. If you like your bull and can separate his offspring from him, them you could keep him longer.
This seems like a lot and is just some of the conclusions that we came to for our situation. I would recommend doing your own research to make sure if fits your needs or if you find a better way. I hope it helps and good luck with the Highlands!
That's kind of along the lines of what I've been thinking.
I would like to keep purebred, not necessarily registered...
Thanks for sharing that info @knowledge-seeker